Patent GB-912799-A (GB)
Title: Improvements in or relating to the growth of single crystals of synthetic garnets, ferrites and orthoferrites
IPC: C30B9/12
Filed: 1961-05-11
Abstract: Single crystals of sythetic garnets, ferrites or orthoferrites are crystallized from a flux comprising lead oxide and boron oxide.  The garnets have a general formula M3Me5O12 where Me is Fe+++ which may be mixed in part with at least one of the elements Ga, Al, Sc, Cr, or Co, and M is yttrium, or a rare earth element of atomic number 62 to 71; the orthoferrites have a general formula XFeO3 where X is yttrium, lanthanum, praseodymium, neodymium, or a rare earth element of atomic number 62 to 71, corresponding compounds of formula XZO3 where Z is Co, Cr, Ga or Al may be similarly prepared; the ferrites concerned are spinels of formula MMe2O4 where M is a divulent metal such as Mn, Fe, Co, Ni, Cu, Zn, Mg or Cd and Me is Fe or Al.  The ferrites of Mg, Ni, Co, Al, Zn, and Cd (magnetic spinels) and Mg Al and Ga (non-magnetic spinels) are also referred to.  The materials are produced by dissolving suitable amounts of the oxides in a flux of lead oxide and boron oxide, and crystallizing the resulting product.  In the preparation of a synthetic garnet the weight ratio of lead oxide to boron oxide is 9:1 to 14:1 (preferably 10:1), and the ratio of gross nutrient to flux 1:1,8 to 1:2,2. The mixture may be heated to 1300 DEG C., and cooled at the rate of 1/2  DEG  to 10 DEG C. per hour to approximately 1000 DEG C. when the liquid portion of the flux is removed, in order to avoid resolution of the garnet crystals.  It is possible to avoid this re-solution by rapid cooling from approximately 1000 DEG C. to complete solidification.  The crystals remaining are air cooled to room temperature, and the flux residue is dissolved in 50% boiling nitric acid, and the garnet crystals washed with boiling distilled water, and air-dried at room temperature.  In the examples yttrium iron garnet (Y3Fe5O12), gadolinium gallium garnet (Gd3Ga5O12), gadolinium iron garnet (Gd3Fe5O12), ylterbium iron garnet (Yb3Fe5O12), yttrium erbium iron garnet ((YEr)3 Fe5O12),  and yttrium gallium iron garnet (Y3(Ga4-95Fe0,05)O12) are prepared.  For or more rare earths are added to yttrium iron garnet; 100% excess must be included to allow for loss of the additive in the flux.  Aluminium may be similarly included. Orthoferrites are prepared by using 18:1 to 22:1 lead oxide boron oxide flux, and a gross nutrient to flux ratio of 1:2,8 to 1:3,2.  The procedure is the same as for garnets but without the step of removing liquid flux at 1000 DEG C.  These materials may be modified by the inclusion of small amounts of additional ingredients e.g. aluminium.  In the examples yttrium orthoferrite (YFeO3), lanthanum orthoferrite (LaFeO3), and holmium orthoferrite (HoFeO3) are prepared.  In general all the considerations for the orthoferrites apply to the spinels also, except that the ratio of nutrient to flux may vary from one spinel to another.  1:4 is a suitable ratio for nickel spinel, 1:5 for magnesium ferrites, 1:2 for cobalt spinel, 1:4 for cadmium and zinc, spinels and 1:7 for magnesium aluminium spinels.  In the examples NiFe2O4, MgFe2O4, and MgAlFeO4 are prepared.  Specification 783,670 is referred to.